1. Field of the Invention
This invention relates to a medium for electrophoresis, and more particularly relates to a medium for electrophoresis suitably employable for determination of base sequence of DNA, RNA, their fragment, and their derivatives.
2. Description of Prior Arts
In the method for determination of the base sequence of DNA, RNA, their fragments, and their derivatives according to the post-label method, the operation of slab electrophoresis using a polyacrylamide gel membrane (medium) has become essential. Since the study in the genetic engineering technology has greatly advanced recently, quick determination of the base sequence of DNA, etc. is highly desired.
The polyacrylamide gel membrane employable for the above purpose can be prepared by crosslinking polymerization of a monomer such as acrylamide and a two-functional crosslinking agent such as N,N'-methylenebisacrylamide under an oxygen-free condition in the presence of water and a polymerization catalyst. In the course of the preparation of the polyacrylamide gel membrane, a modifier such as urea or formamide is generally incorporated into the membrane.
Since the polymerization reaction for the preparation of polyacrylamide is a radical crosslinking polymerization as described above, the polymerization can be easily inhibited by the presence of oxygen. Therefore, the gel membrane should be prepared in the absence of oxygen. For this reason, a polyacrylamide gel membrane is generally prepared by a process involving: introducing an aqueous solution (gel-forming solution or gel solution) containing acrylamide, a crosslinking agent and a polymerization catalyst into a cell formed between two glass plates with a certain clearance (e.g., 0.3-1 mm); sealing the gel-forming solution from oxygen; and causing the crosslinking polymerization to prepare the desired gel membrane.
The cell employed for the preparation of the gel membrane generally has length of approx. 40 to 100 cm. Accordingly, the introduction of the gel-forming solution into the such a long cell requires careful operation to prevent the solution from foaming. However, if a long period of time is employed for the introduction of the gel-forming solution into the cell, the gelation advances prior to completion of the introduction, whereby failing to prepare a polyacrylamide gel membrane of the desired length. Thus, the preparation of a polyacrylamide gel having the desired length requires highly skilled operation, as well as the operation keeping the solution from oxygen. This is one reason to make it difficult to prepare the polyacrylamide gel membrane (medium) in a mass scale.